Supplemental heating in waste heat recovery

ABSTRACT

A waste heat recovery apparatus, for use with an internal combustion engine, includes a working fluid circuit to circulate working fluid, a boiler connected on the working fluid circuit and adapted to recover waste heat from a source to heat working fluid, and an expander connected on the working fluid circuit to receive working fluid from the boiler. A supplemental heating arrangement is connected on the working fluid circuit to selectively heat the working fluid when recovered waste heat is not sufficient to heat the working fluid to an operating temperature for the expander.

FIELD OF THE INVENTION

The invention relates to bottoming cycle apparatuses, such as Rankine cycle apparatuses, for recovering energy from waste heat of internal combustion engines, and more particularly, to a method and apparatus for ensuring the working fluid is at a temperature sufficient for operation of the waste heat expander.

BACKGROUND AND SUMMARY

For a bottoming cycle apparatus, such as an apparatus based on the Rankine cycle, system efficiency is related directly to the up-time, that is, the operational time during which recovery of waste heat occurs. Inactive periods are often due to poor quality heat being available (not enough waste heat) or due to component warm-up time (when boilers and expansion machines are warming up). For example, a waste heat recovery apparatus connected to a truck engine may be inactive immediately after the engine is started and is warming up.

The invention proposes a solution to increase operational time by improving thermal management during periods of poor quality heat availability and to decrease the warm up time of the apparatus when returning to operation.

The invention is applicable to bottoming cycles such as the Rankine cycle, the Ericsson cycle and other waste heat recuperating cycles.

A bottoming cycle apparatus may include an expansion machine connected in a working fluid circuit to receive working fluid from a waste heat recovery heat exchanger, such as a boiler, vaporizer, or heat exchanger. The working fluid directed to an expansion machine is expanded in the expansion machine to generate usable work or energy.

According to the invention, a heating arrangement operatively connected on the working fluid circuit provides supplemental heat to the working fluid when the waste heat recovered by the waste heat recovery heat exchanger is not sufficient to raise the working fluid enthalpy to a working level for the expander.

The heating arrangement may include a burner or an electrical heating device arranged with a heat exchanger to heat the working fluid. A burner may include a source of fuel, for example, a hydrocarbon fuel such as diesel. An electrical heating device may be connected to receive electrical energy from a source such as a vehicle electrical supply system.

A controller may be connected to control operation of the heating device and connected monitor temperature and pressure of the working fluid (which may be measured at the outlet of the boiler).

The heating arrangement may be positioned on the working fluid circuit between the boiler and the expander. Alternatively, the heating arrangement may be positioned on the working fluid circuit between the pump and the boiler.

According to yet another alternative, the heating arrangement may be positioned on the boiler to add heat to the waste heat source flow. For example, if the boiler is connected to receive a flow of engine exhaust gas as the waste heat source, the supplemental heating arrangement may be disposed to add heat to the exhaust gas as it enters the boiler.

According to the invention, the working fluid circuit may include a heating loop on which the supplemental heating arrangement is disposed, the heating loop controlled by a valve, the valve directing working fluid directly to the expander or to the heating loop before entry in the expander responsive to the heat quality of the working fluid.

According to yet another aspect, the working fluid circuit may include a bypass circuit around the expansion machine through which working fluid is directed when the heat quality is low or when operation of the expander is not desired.

According to an embodiment, the bypass circuit may include a first loop, or heating loop, on which the supplemental heating arrangement may be disposed and which returns working fluid to the expander and a second loop that directs working fluid from the first loop to bypass the expander.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a typical Rankine cycle apparatus according the prior art.

FIG. 2 is a schematic view of a Rankine cycle apparatus having a bypass circuit to allow working fluid to bypass the expansion machine.

FIG. 3 is a schematic view of a bottoming cycle apparatus according to an embodiment of the invention in which a supplemental heating arrangement is provided to selectively add heat to the working fluid.

FIG. 4 is a schematic view of an alternative embodiment of the apparatus of FIG. 3 including a bypass circuit around the expansion machine.

FIG. 5 is a schematic view of another alternative embodiment of the apparatus of FIG. 3, including a first bypass circuit on which a supplemental heating arrangement is provided and a second bypass circuit around the expansion machine.

FIG. 6 is a schematic view of a bottoming cycle apparatus according to an alternative embodiment in which the heating arrangement is provided upstream of the boiler.

FIG. 7 is a schematic view of a bottoming cycle apparatus according to yet an alternative embodiment in which the heating arrangement is provided on the waste heat inlet to the boiler.

DETAILED DESCRIPTION

As seen in FIG. 1, a typical bottoming cycle waste heat recovery apparatus includes a vaporizer or boiler 10 to recover heat from a heat source (not illustrated), such as waste heat from an internal combustion engine exhaust, engine coolant, engine oil cooler, or other source, to heat a working fluid. An inflow line 11 at a boiler inlet conducts the waste heat-carrying medium (e.g., exhaust gas) into the boiler 10 and an outflow line 13 carries the medium out after heat exchange from the boiler outlet. Working fluid is carried through the waste heat recovery apparatus by a working fluid circuit 12. The heated working fluid exiting the boiler 10 is directed through a working fluid circuit line 12 a to an expansion machine or expander 14, which generates work by expanding the working fluid. The expander may be a turbine, a piston engine, a scroll, a screw, or other machine. The generated work may be transmitted through a shaft 15, and may be used, for example, to drive an electrical generator or as mechanical power added to the drive shaft of the internal combustion engine. Expanded working fluid is directed through the circuit line 12 b to a condenser 16, which removes residual heat from and condenses the working fluid. The condensed fluid is then directed through a circuit line 12 c to a pump 18, which compresses the working fluid. A circuit line 12 c carries the working fluid from the pump 18 to the boiler 10 to repeat the waste heat recovery cycle.

As seen in FIG. 2, and as known in the art, a bottoming cycle waste heat apparatus may include a bypass valve 20 and bypass circuit 22 to selectively direct working fluid around the expander 14 to the condenser 16. The bypass valve 20 may be controlled to direct the working fluid to the expander 14 through line 24 when the working fluid is at operational condition, or through line 22 to bypass the expander 14 when power generation by the expander is not desired or when the quality of the working fluid is not sufficient for expansion. The quality of the working fluid may not be sufficient when there is not enough waste heat available at the boiler 10 to heat the working fluid to an operational temperature, for example, as superheated steam. The condenser 16 cools the working fluid received from the bypass circuit and the cooled fluid is pumped by the pump 18 to the vaporizer/boiler 10.

FIG. 3 illustrates an embodiment of an apparatus according to the invention. The apparatus of FIG. 3 includes a heating arrangement 40 operatively connected on the working fluid circuit 12 to provide supplemental heat to the working fluid. The heating arrangement 40 is illustrated as connected between the vaporizer 10 and the expander 14. When the heat recovered by the vaporizer 10 and transferred to the working fluid is not sufficient for use in the expander 14, the heating arrangement 40 may be operated to add supplemental heat to the working fluid.

The heating arrangement 40 may be configured as a heat exchanger with heat being supplied by a burner or electric heating device.

The heating arrangement 40 is connected to receive energy from an energy source 44. The heating arrangement 40 may be a burner arrangement and the energy source 44 may be a hydrocarbon fuel. The fuel conveniently may be the same fuel as is used by an engine generating the waste heat. The heating arrangement 40 may alternatively be an electrical heater and the energy source configured as an electrical energy source. For example, if the waste heat recovery apparatus is associated with a truck, the truck's electrical system may be connected as the energy source. Other heating arrangements may be used.

The heating arrangement 40 may be operated based on a sensed temperature of the working fluid exiting the boiler 10. A temperature sensor 46 at the outlet of the boiler 10, or on the working fluid circuit 12 a on the outlet side of the boiler, may be connected to provide a temperature signal to a controller 48, which is connected to control the heating arrangement 40 and the energy source 44 responsive to the temperature signal from sensor 46.

The heating arrangement 40 may also be controlled based on other operational conditions, such as pressure of the working fluid. In addition, a temperature sensor 62 on the outlet side of the expander (or at the inlet of the condenser) can monitor temperature of the exiting, expanded working fluid and provide a signal the controller 48.

FIG. 4 is a schematic view of an alternative embodiment the apparatus of FIG. 3. A bypass valve 20 is provided to direct working fluid through a bypass circuit 22 to bypass the expansion machine 14 when the heat quality is not sufficient for expansion. The bypass valve 20 is controlled to direct working fluid to the expansion machine 14 when the heat quality of the working fluid, from recovered waste heat from the boiler 10, from supplemental heat from the heating arrangement 40, or from both, is sufficient for expansion. The bypass valve 20 is controlled by the controller 48 responsive to conditions including the temperature of the working fluid measured by sensor 46 at the outlet side of the boiler and/or by sensor 47 at the outlet side of the heating arrangement 40.

FIG. 5 shows another alternative embodiment that includes a first bypass valve 20 a to direct working fluid to the expansion machine 14 if the heat quality of the working fluid flowing from the boiler 10 is of sufficient quality or, if supplemental heating is required, to a first bypass circuit 22 a on which a supplemental heating arrangement 40 is disposed. A second bypass valve 20 b is downstream of the heating arrangement 40 and directs working fluid through circuit 22 b to the expansion machine 14 if the heat quality of the working fluid is sufficient for expansion, thus completing the first bypass circuit. The second bypass valve 20 b directs working fluid through a second bypass circuit 22 c if the heat quality of the working fluid is not sufficient for expansion. The first bypass valve 20 a and second bypass valve 20 b are controlled by controller 48 responsive to operating conditions, including the temperature of the working fluid as measured by sensor 46 on the outlet side of the boiler 10 and the sensor 47 on the outlet side of the heating arrangement 40.

According to an alternative embodiment of FIG. 5, the second bypass valve 20 b and second bypass circuit 22 c are omitted and the first bypass valve 20 a, bypass circuit 22 a, and heating arrangement 40 comprise a heating loop. The bypass valve 20 a is controlled to direct working fluid directly to the expander or to the heating loop for supplemental heating prior to the working fluid being directed to the expander.

FIG. 6 is a schematic of an alternative embodiment. The heating arrangement 40 may be connected to the working fluid circuit 12 on the inlet side of the boiler 10, between the pump 18 and the boiler 10. A bypass valve 20 and bypass circuit 22 may also be provided to direct working fluid to bypass the expander if operation of the expander is not desired or if the quality of the working fluid is not sufficient for expansion.

FIG. 7 is a schematic of another alternative arrangement, in which the heating arrangement 40 is connected on the waste heat inlet line 11 of the boiler 10. A bypass valve 20 and bypass circuit 22 may also be provided as in the other embodiments.

The invention has been described in terms of preferred principles, embodiments, and components. Those skilled in the art will understand that substitutions may be made for the components shown without departing from the scope of the invention as defined by the appended claims. 

1. A waste heat recovery apparatus, comprising: a working fluid circuit to circulate working fluid; a boiler connected on the working fluid circuit and adapted to recover waste heat from a source and transfer recovered waste heat to the working fluid; an expander connected on the working fluid circuit to receive working fluid from the boiler; and, a supplemental heating arrangement connected to deliver heat to the working fluid.
 2. The waste heat recovery apparatus of claim 1, comprising: a temperature sensor disposed to sense a temperature of the working fluid at an exit of the boiler and generate a temperature signal representative thereof; and, a controller connected to receive the temperature signal from the temperature sensor and connected to control the heating arrangement responsive to the temperature signal.
 3. The waste heat recovery apparatus of claim 1, comprising an energy source connected to deliver energy to the heating arrangement.
 4. The waste heat recovery apparatus of claim 1, comprising a burner in the heating arrangement.
 5. The waste heat recovery apparatus of claim 1, comprising an electric heater in the heating arrangement.
 6. The waste heat recovery apparatus of claim 1, wherein, the supplemental heating arrangement is connected to the working fluid circuit between the boiler and the expander.
 7. The waste heat recovery apparatus of claim 1, wherein, the supplemental heating arrangement is connected to the working fluid circuit between the pump and the boiler.
 8. The waste heat recovery apparatus of claim 1, wherein, the supplemental heating arrangement is connected to deliver heat to the boiler.
 9. The waste heat recovery apparatus of claim 1, comprising: a temperature sensor disposed to sense a temperature of the working fluid at an exit of the supplemental heating arrangement and generate a temperature signal representative thereof; and, a controller connected to receive the temperature signal from the temperature sensor and connected to control the heating arrangement responsive to the temperature signal.
 10. The waste heat recovery apparatus of claim 1, comprising a bypass valve and bypass circuit connected on the working fluid circuit to selectively direct working fluid to bypass the expander.
 11. The waste heat recovery apparatus of claim 10, wherein the supplemental heating arrangement is connected in the working fluid circuit between the boiler and the bypass valve.
 12. The waste heat recovery apparatus of claim 10, comprising a second bypass valve, the bypass circuit comprising a first circuit wherein working fluid flows is directed by the first bypass valve to the second bypass valve then by the second bypass valve to the expander and a second bypass circuit wherein working fluid is directed by the first bypass valve to the second bypass valve then by the second bypass valve to bypass the expander.
 13. The waste heat recovery apparatus of claim 12, wherein the supplemental heating arrangement is disposed on the first circuit.
 14. The waste heat recovery apparatus of claim 1, comprising a valve connected on the working fluid circuit to selectively direct working fluid to one of the expander or to a heating loop, wherein the supplemental heating arrangement is disposed on the heating loop. 